Ultrasound imaging device, ultrasonic probe, and transmission device

ABSTRACT

An ultrasonic imaging apparatus includes a plurality of transducers that transmit ultrasonic waves and a transmission unit that supplies drive signals to the plurality of transducers. An amplitude control voltage generation unit and a transmission circuit unit are connected to a common voltage power supply. An amplitude control voltage generation unit receives an output voltage of the voltage power supply and an attenuation degree setting signal instructing an attenuation degree of the drive signal for each of the transducers for weighting of the drive signal, and generates an amplitude control voltage corresponding to a voltage obtained by attenuating the output voltage by the attenuation degree. The output voltage of the voltage power supply is reduced to a voltage corresponding to the amplitude control voltage, and a drive signal having a predetermined waveform is generated whose amplitude is the voltage after the reduction for each of the transducers.

TECHNICAL FIELD

The present invention relates to an ultrasonic imaging apparatus capableof weighting amplitudes of a drive signal.

BACKGROUND ART

An ultrasonic diagnostic apparatus is widely used as a medical diagnosisapparatus that can perform observation non-invasively and in real time.Further, in recent years, in addition to a two-dimensional image in therelated art, a three-dimensional stereoscopic image and the like canalso be displayed, and the use thereof is steadily increasing. On theother hand, resolution of image quality is lower than that of an X-raycomputed tomography (CT) apparatus or a magnetic resonance imaging (MRI)apparatus, and therefore higher image quality is demanded than everbefore.

The ultrasonic diagnostic apparatus transmits an ultrasonic beam to asubject from an ultrasonic probe incorporating a plurality oftransducers arranged one-dimensionally or two-dimensionally, receivesechoes from the subject with a plurality of ultrasonic elements, andgenerates an ultrasonic image based on the obtained reception signal.

PTL 1 discloses a structure for transmitting an ultrasonic pulse whoseamplitude changes in a sine wave shape in a time axis direction in orderto reduce a harmonic component included in an ultrasonic beam and toimprove image quality of an image obtained by a harmonic echo method.Specifically, a pulse generation circuit is connected to thetransducers. The pulse generation circuit changes an amplitude stepwiseby sequentially turning on and off a plurality of switching elementsconnected to a plurality of power supplies having different voltages,generates a pulse signal having an envelope with a sine wave shape, andsupplies the pulse signal to an ultrasonic element.

PTL 2 discloses an apparatus including a transmission circuit forsupplying a drive signal with a set amplitude to a transducer for eachtransducer. The transmission circuit is disposed in an ultrasonic probe,and changes a magnitude of the drive signal according to a signalintensity of an amplitude setting signal received from an apparatus mainbody.

Further, since the ultrasonic diagnostic apparatus is limited toultrasonic energy that can be radiated to the human body, it is commonto change an amplitude of an ultrasonic pulse in the case of imaging aB-mode image and in the case of imaging a color Doppler image in which aplurality of ultrasonic pulses need to be transmitted at the sameposition. In addition, the amplitude of the ultrasonic pulse needs to bechanged depending on a size and a depth of a diagnosis region.

RELATED ART LITERATURE Patent Literature

PTL 1: JP-A-9-234202

PTL 2: WO 2015/186234 (in particular, paragraphs 0044 to 0050)

SUMMARY OF INVENTION Technical Problem

In the ultrasonic diagnostic apparatus, in order to obtain ahigh-quality ultrasonic image, it is desirable to reduce side lobesappearing on both sides of a main lobe of an ultrasonic beam. In orderto reduce the side lobes, when a transmission amplitude of a transducerat the center position of the main lobe is set to 100%, it is desiredthat amplitudes of a drive signal for each transducer are weighted(apodization) so as to gradually reduce the transmission amplitude ofthe transducer to 80% and 40% as the transducer is away from atransmission center. Further, not only the amplitude is reducedaccording to a position of the transducer in order to reduce the sidelobes, but also weighting according to the arrangement of the transduceris required in order to avoid the occurrence of a grating lobe.

When the ultrasonic beam scanning is performed while weighting theamplitudes to reduce the side lobes, it is necessary to change theweight of the amplitudes of the drive signal of each transducer everytime a position or direction of the main lobe is shifted.

Further, when the amplitude of the ultrasonic pulse is changed in orderto switch between B-mode imaging and color Doppler imaging, if aposition of the ultrasonic pulse does not change, a weighting ratioitself does not need to be changed. However, since the amplitude of theultrasonic pulse itself is changed, it is necessary to change theamplitude of the drive signal of each transducer. In particular, in thecase of an imaging method of alternately transmitting an ultrasonic beamfor the B-mode imaging and the color Doppler imaging in one second andsimultaneously displaying both images, it is necessary to change atransmission amplitude of the same transducer several times per second.

As a configuration for weighting the amplitudes of the drive signal foreach transducer, for example, as in PTL 1, a technique of preparing aplurality of types of power supply voltages and selecting a power supplyvoltage may be applied. However, in the technique, a wiring thatconnects the plurality of types of power supply voltages for eachtransducer and a switch that selects any of the plurality of types ofpower supply voltages according to the weighted amplitude for each powersupply voltage are required. Therefore, circuit scale of a generationcircuit of the drive signal increases. Further, a calculation unit thatcalculates the weighted amplitude for each transducer each time theultrasonic beam is transmitted, and a control unit that determines whichpower supply voltage should be selected and turns on the switch are alsorequired.

Further, as in the transmission circuit described in PTL 2, it is alsoconceivable to apply a technique of changing a magnitude of the drivesignal according to a magnitude of an amplitude setting signal receivedfrom the apparatus main body, thereby weighting the amplitudes of thedrive signal for each transducer. However, even in the case of applyingthis technique, each time the B-mode imaging and the color Dopplerimaging are switched, and each time the ultrasonic beam scanning isperformed, required is a calculation unit that calculates anappropriately weighted amplitude magnitude for each transducer,generates an amplitude setting signal having the magnitude as a signalintensity and outputs the amplitude setting signal to the transmissioncircuit of each transducer.

In this way, when attempting to weight the drive signal for eachtransducer in order to reduce the side lobes by applying the techniqueof PTL 1, the circuit scale of the switch, the wiring, and the likeincreases. In both PTLs 1 and 2, a calculation unit that calculates theweighted amplitude for each transducer, a control unit, and the like arerequired, and a scale of a calculation processing unit is alsoincreased. Therefore, a problem arises in that the size of an ultrasonicimaging apparatus increases.

An object of the invention is to perform weighting for a drive signalfor each transducer without re-calculating an amplitude of the drivesignal for each transducer even when an intensity of an ultrasonic beamis changed.

Solution to Problem

In order to achieve the above object, the invention provides thefollowing ultrasonic imaging apparatus. That is, an ultrasonic imagingapparatus of the invention includes a plurality of transducers thattransmit ultrasonic waves and a transmission unit that supplies drivesignals to the plurality of transducers. The transmission unit includesan amplitude control voltage generation unit and a transmission circuitunit. The amplitude control voltage generation unit and the transmissioncircuit unit are connected to a common voltage power supply. Theamplitude control voltage generation unit receives an output voltage ofthe voltage power supply and an attenuation degree setting signalinstructing an attenuation degree of the drive signal for each of thetransducers for weighting for the drive signal, and generates anamplitude control voltage corresponding to a voltage obtained byattenuating the output voltage of the voltage power supply by theattenuation degree. The transmission circuit unit reduces an absolutevalue of the output voltage of the voltage power supply to a valuecorresponding to the amplitude control voltage, and generates a drivesignal having a predetermined waveform whose amplitude is the voltageafter the reduction for each of the transducers.

Advantageous Effect

According to the invention, even when the intensity of the ultrasonicbeam is changed, the weighting for each transducer can be performedwithout re-calculating the amplitude of the drive signal for eachtransducer.

Problems, configurations, and effects other than those described abovewill become apparent from the following description of the embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an overall configuration of anultrasonic imaging apparatus according to an embodiment of theinvention.

FIG. 2 is a block diagram showing a configuration of a transmission unit120 of the ultrasonic imaging apparatus of FIG. 1.

FIG. 3 is a block diagram showing a more detailed configuration of thetransmission unit 120 of FIG. 2.

FIG. 4 is a circuit diagram of an amplitude control voltage generationunit 100 of the ultrasonic imaging apparatus according to a firstembodiment.

FIG. 5 is a circuit diagram of a transmission circuit unit 102 of theultrasonic imaging apparatus according to the first embodiment.

FIG. 6 is a block diagram showing a configuration of the transmissionunit 120 of an ultrasonic imaging apparatus according to a secondembodiment.

FIG. 7 is a circuit diagram of the amplitude control voltage generationunit 100 of the ultrasonic imaging apparatus according to the secondembodiment.

FIG. 8 is a circuit diagram of the transmission circuit unit 102 of theultrasonic imaging apparatus according to the second embodiment.

FIG. 9 is a block diagram showing a configuration of the transmissionunit 120 of an ultrasonic imaging apparatus according to a thirdembodiment of the invention.

FIG. 10 is a circuit diagram showing a configuration of the amplitudecontrol voltage generation unit 100 of the ultrasonic imaging apparatusaccording to the third embodiment.

FIG. 11 is a block diagram showing an appearance of an ultrasonicdiagnostic apparatus according to a fourth embodiment of the invention.

FIG. 12 is a block diagram showing an appearance of an ultrasonicdiagnostic apparatus according to a fifth embodiment of the invention.

FIG. 13 is an explanatory diagram showing an arrangement of an analogfront end circuit 41 connected to a transducer 103 according to thefourth and fifth embodiments.

FIGS. 14(a) and 14(b) are explanatory diagrams showing distribution oftransmission signal levels (amplitudes) of the transducer 103 accordingto the fourth and fifth embodiments at times t1 and t2.

DESCRIPTION OF EMBODIMENTS

In the following embodiments, description may be divided into aplurality of sections or embodiments if necessary for convenience.Unless particularly specified, these embodiments are not independentwith each other, but in a relationship in which one embodiment is avariation, detailed description, supplementary description, or the likeof a part or all of another embodiment. In the following embodiments,when the number and the like (including number of article, numericvalue, quantity, or range) of an element are referred to, theseparameters are not limited to the specific numbers, and the values maybe greater or less than these specific numbers, unless particularlyspecified or unless the specific numbers are apparently limited tospecific numbers in principle.

Further, in the following embodiments, it is needless to say that theconstituent elements (including element steps) are not necessarilyessential, unless particularly specified or considered to be apparentlyessential in principle. Similarly, in the following embodiments, whenreferring to shapes, positional relationships, and the like of theconstituent elements and the like, shapes and the like which aresubstantially approximate or similar to those are included, unlessparticularly specified or considered to be apparently excluded inprinciple. The same also applies to the numeric value and the rangesdescribed above.

Hereinafter, an ultrasonic imaging apparatus according to embodimentswill be described with reference to the drawings. In all the drawingsfor illustrating the embodiments, the same configuration are denoted bythe same reference numerals in principle, and the repetitive descriptionthereof will be omitted.

FIG. 1 shows an example of a schematic configuration of an ultrasonicimaging apparatus according to the present embodiment. FIG. 2 shows aconfiguration of a transmission unit 120. As shown in FIGS. 1 and 2, anultrasonic imaging apparatus 300 of the present embodiment includes aplurality of transducers 103 that transmit ultrasonic waves, and thetransmission unit 120 that supplies drive signals to each of theplurality of transducers 103. The transmission unit 120 includes anamplitude control voltage generation unit 100 and a transmission circuitunit 102. The amplitude control voltage generation unit 100 and thetransmission circuit unit 102 are connected to a common voltage powersupply 121.

The amplitude control voltage generation unit 100 receives an outputvoltage of the voltage power supply 121 and an attenuation degreesetting signal instructing an attenuation degree of a drive signal foreach transducer 103, and generates an amplitude control voltagecorresponding to a voltage obtained by attenuating the output voltage ofthe voltage power supply 121 by the attenuation degree indicated by theattenuation degree setting signal.

The transmission circuit unit 102 reduces an absolute value of theoutput voltage of the voltage power supply 121 to a value correspondingto the amplitude control voltage, and generates a drive signal having apredetermined waveform whose amplitude is the voltage after thereduction for each transducer. The generated drive signal is output toeach transducer 103.

In this way, in the present embodiment, the attenuation degree for eachtransducer indicated by the attenuation degree setting signal isreceived, and the amplitude control voltage corresponding to the voltageobtained by attenuating the output voltage of the voltage power supply121 by the attenuation degree is generated for each transducer, so thatamplitudes of the drive signal can be weighted. Thus, by setting theattenuation degree according to the position of the transducer, forexample, by gradually increasing the attenuation degree as thetransducer is away from the at the center without attenuating thetransducer at the center of the ultrasonic beam, the amplitudes of thedrive signal can be weighted according to the position of the transducerwhile reducing or increasing an overall output of the ultrasonic beam bysimply changing the output voltage of the voltage power supply 121.

Accordingly, an output of each transducer can be weighted, for example,gradually decreasing the output as the transducer is away from thecenter of an ultrasonic beam while changing the output of the ultrasonicbeam according to the change of an imaging mode, so that side lobes ofthe ultrasonic beam can be prevented.

In the present embodiment, even when the intensity of the ultrasonicbeam is changed by changing the imaging mode a plurality of times in onesecond, unlike the related art, it is not necessary to calculate anattenuated (weighted) amplitude voltage for every change or set anamplitude setting signal, and only a power supply voltage should bechanged. Therefore, it is possible to reduce a scale of the calculationcircuit and the control circuit and the number of cables, and to providean ultrasonic imaging apparatus having a small size and a simpleconfiguration.

When weight distribution is changed according to the position of thetransducer, for example, in the case of ultrasonic beam scanning, anattenuation degree setting signal instructing the attenuation degree foreach transducer may be changed, and it is not necessary to calculate theattenuated amplitude voltage.

The transmission circuit unit 102 and the amplitude control voltagegeneration unit 100 may be disposed for each transducer 103.

A transmission control unit 101 that generates an attenuation degreesetting signal for each transducer 103 and outputs the signal to theamplitude control voltage generation unit 100 may be disposed in thetransmission unit 120.

Hereinafter, the ultrasonic imaging apparatus of the present embodimentwill be described in more detail.

First Embodiment

An ultrasonic imaging apparatus according to a first embodiment of theinvention will be described in detail.

As shown in FIG. 1, the ultrasonic imaging apparatus 300 according tothe first embodiment includes a reception unit 105, a transmission andreception separation unit 104, a control unit 122, and an imageprocessing unit 106 in addition to the plurality of transducers 103, thetransmission unit 120, and the voltage power supply 121. The voltagepower supply 121 is a variable voltage power supply capable of changinga voltage to be output.

As to be described in detail below, the transmission unit 120 generatesa drive signal weighted for each transducer 103 from a voltage suppliedfrom the variable voltage power supply 121, outputs the drive signal tothe transducer 103, and causes the transducer 103 to transmit anultrasonic beam to an imaging region of a subject (not shown). Anintensity of the ultrasonic beam is changed depending on an imagingmode. When the imaging mode is simultaneous imaging of a B-mode and acolor Doppler, an ultrasonic beam having an intensity set for eachimaging is alternately emitted. The ultrasonic beam is reflected by thetissue of the subject to generate an echo, and the echo is received byeach transducer 103 of a probe 130. The control unit 122 controls thetransmission unit 120 and the variable voltage power supply 121.

When the imaging mode is the B-mode, the reception unit 105 performs aprocessing of adding after delaying a reception signal output from eachtransducer 103 (reception beamforming) so as to generate focus data fora plurality of reception focuses set in the imaging region. When theimaging mode is the color Doppler, the reception unit 105 calculates aDoppler frequency for each reception focus by using a signal obtained bytransmitting and receiving the ultrasonic wave for a plurality of timesin order to obtain blood flow information. When the imaging mode is theB-mode, the image processing unit 106 generates a B-mode image of theimaging region by setting a value of focus data of the reception focusto a pixel value of a pixel at a position of the reception focus. Whenthe imaging mode is the color Doppler, the image processing unit 106assigns a color corresponding to the Doppler frequency to the pixel atthe position of the reception focus, and generates a color Dopplerimage. When the imaging mode is both the B-mode and the color Doppler,both images are generated. The generated image is displayed on a displayunit 107 connected to the image processing unit 106.

The transmission and reception separation unit 104 separates the drivesignal output from the transmission unit 121 to the transducer 103 andthe reception signal output by the transducer 103.

The transmission unit 120 will be described in more detail. As shown inFIG. 2, the transmission unit 120 includes a transmission control unit101 in addition to the amplitude control voltage generation unit 100that generates the amplitude control voltage and the transmissioncircuit unit 102. The amplitude control voltage generation unit 100 andthe transmission circuit unit 102 are disposed for each transducer 103.The amplitude control voltage generation unit 100 and the transmissioncircuit unit 102 are both connected to the common variable voltage powersupply 121. The transmission control unit 101 generates an attenuationdegree setting signal and a transmission control signal, and outputs thesignals to the amplitude control voltage generation unit 100 and thetransmission circuit unit 102.

FIG. 3 shows structures of the amplitude control voltage generation unit100 and the transmission circuit unit 102.

The amplitude control voltage generation unit 100 includes a referencevoltage generation unit 1 that generates a reference voltage from anoutput voltage of the voltage power supply 121, a voltage-currentconversion unit 2 that converts the reference voltage into a current, acurrent control unit that sets the current obtained by conversion of thevoltage-current conversion unit 2 according to an attenuation degreesetting signal, and a current-voltage conversion unit 4 that generatesan amplitude control voltage by converting the current set by thecurrent control unit 3 into a voltage. The transmission circuit unit 102includes an amplitude control unit 5 that reduces the output voltage ofthe variable voltage power supply to a voltage corresponding to theamplitude control voltage, and a drive circuit unit 6 that generates adrive signal of a predetermined pulse waveform whose amplitude is thevoltage after the reduction. At this time, even when the voltage of thevariable voltage power supply 121 is fluctuated, the amplitude controlvoltage is a voltage proportional to the power supply voltage in whichthe power supply voltage is attenuated by an attenuation degreeindicated by the attenuation degree setting signal, so that amplitudecontrol reflecting the magnitude of the power supply voltage and theattenuation degree (weighting) can be performed. In the presentembodiment, each of the above units 1 to 6 is constituted by, forexample, an analog circuit.

A specific circuit configuration example of the amplitude controlvoltage generation unit 100 is shown in FIG. 4.

The reference voltage generation unit 1 has a configuration in which aresistor 10 having a resistance value R₁ and a resistor 11 having aresistance value R₂ are connected in series, and an output terminal isconnected to a wiring between the resistor 10 and the resistor 11. Theresistor 10 is connected to the variable voltage power supply 121. Whenthe voltage of the variable voltage power supply 121 is expressed asHVDD, a reference voltage V₀ obtained by resistance-dividing the powersupply voltage HVDD is output from the output terminal as in thefollowing Formula (1).V ₀=HVDD×R ₂/(R ₁ +R ₂)  (1)

The voltage-current conversion unit 2 includes an operational amplifier(OPAMP) 12, an N-type MOS (NMOS) transistor 13, and a reference resistor14 having a resistance value R_(ref)′. The reference voltage V₀ outputfrom the reference voltage generation unit 1 is input to a plus terminalof the OPAMP 12. The output of the OPAMP 12 is connected to a gateterminal of the NMOS transistor 13. A source terminal of the NMOStransistor 13 is connected to the reference resistor 14 and a minusterminal of the OPAMP 12 to form a feedback loop. The other terminal ofthe reference resistor 14 is grounded. An output of the voltage-currentconversion unit 2 having such a circuit configuration serves as a drainterminal of the NMOS transistor 13.

With the feedback loop, a voltage V₀′ of the minus terminal of the OPAMP12 is equal to the reference voltage V₀, which is an input signal of theplus terminal. Since the voltage V₀′ is also connected to the referenceresistor 14, a current I₀ flowing through the reference resistor 14 isI₀=V₀′/R_(ref)′. Therefore, the current I₀ is expressed by Formula (2),and is output as an output of the voltage-current conversion unit 2 fromthe drain terminal of the NMOS transistor 13.I ₀ =V ₀ /R _(ref)′  (2)

PMOS transistors 15 and 16 are disposed between the voltage-currentconversion unit 2 and the current control unit 3. The PMOS transistors15 and 16 constitute a current mirror circuit, which converts adirection of the output current I₀ of the voltage-current conversioncircuit 2 and transmits the current to the current control unit 3 in thenext stage.

The current control unit 3 includes a current mirror circuit includingan NMOS transistor 17 and a plurality of NMOS transistors 18 a to 18 n,and switches 19 a to 19 n respectively connected to the NMOS transistors18 a to 18 n. In the circuit configuration of FIG. 4, when the same gatevoltage is applied, the NMOS transistors 18 a to 18 n include the NMOStransistor 18 a through which a current having the same magnitude(amplification factor 1) as the NMOS transistor 17 flows, the NMOStransistor 18 b through which a current twice (amplification factor 2)that of the NMOS transistor 17 flows, . . . , and the NMOS transistor 18n through which a current of N times (amplification factor N) that ofthe NMOS transistor 17 flows. Thus, the transmission control unit 101selectively turns on one or more switches among the switches 19 a to 19n according to an attenuation amount setting signal to turn on one ormore of the NMOS transistors 18 a to 18 n. A current I₀′, which is a sumof currents flowing through the NMOS transistors that are turned on, isoutput from the NMOS transistors 18 a to 18 n as an output of thecurrent control unit 3. Therefore, the current I₀ which is an inputsignal to the current control unit 3 is amplified to the current I₀′ andoutput. When a sum of amplification factors of the NMOS transistors 18 ato 18 n connected to one or more switches turned on according to theattenuation amount setting signal is n, the amplified current I₀′ isexpressed by the following Formula (3).I ₀ ′=n×I ₀  (3)

The current-voltage conversion unit 4 has a circuit configuration inwhich a reference resistor 21 having a resistance value R_(ref),connected to the variable voltage power supply 121, and a high-voltageNMOS transistor 20 are connected in series, and the input current I₀′ isinput to a source terminal of the NMOS transistor 20. An output terminalof an amplitude control voltage is connected to a wiring between thereference resistor 21 and the NMOS transistor 20. The high-voltage NMOStransistor 20 is a protection level shifter of the current control unit3. The output voltage HVDD of the variable voltage power supply 121decreases in response to the input current I₀′, and an amplitude controlvoltage V_(AMP) expressed by the following Formula (4) is output fromthe current-voltage conversion unit 4.V _(AMP)=HVDD−R _(ref) ×I ₀′  (4)

Substituting Formulas (1) to (3) into Formula (4), Formula (5) isobtained.V _(AMP)=HVDD(1−R _(ref) /R _(ref) ′×n×R ₂/(R ₁ +R ₂))  (5)

In the Formula (5), when R_(ref)=R_(ref)′, the Formula (5) is expressedby the following Formula (6).V _(AMP)=HVDD(1−n×R ₂/(R ₁ +R ₂))  (6)

As is apparent from the Formula (6), the amplitude control voltageV_(AMP) is a voltage value obtained by attenuating the output voltageHVDD of the variable voltage power supply 121 at a ratio (n×R₂/(R₁+R₂))proportional to the sum n of the amplification factors of the NMOStransistors 18 a to 18 n connected to one or more switches turned onaccording to the attenuation amount setting signal, and even when theoutput voltage HVDD of the variable voltage power supply 121 fluctuates,the ratio of attenuation (n×R₂/(R₁+R₂)) does not change. For example,when R₂ is 10 kΩ and R₁ is 90 kΩ in the circuit of FIG. 4, the Formula(6) becomes the following Formula (7).V _(AMP)=HVDD(1−0.1n)  (7)

In the Formula (7), when n is 1, V_(AMP)=0.9 HVDD, and when n is 2,V_(AMP)=0.8 HVDD, and the attenuation ratio of the amplitude controlvoltage V_(AMP) becomes large. Even when the power supply voltage HVDDchanges, the attenuation ratio does not change unless the sum n of theamplification factors set according to the attenuation degree settingsignal is changed, and the amplitude control voltage V_(AMP) in whichthe fluctuating power supply voltage HVDD is attenuated by the setattenuation degree can be generated.

Next, a circuit configuration example of the transmission circuit unit102 will be described with reference to FIG. 5. As shown in FIG. 5, thetransmission circuit unit 102 includes the amplitude control unit 5 andthe drive circuit unit 6.

The amplitude control unit 5 is formed of a high-voltage NMOStransistor, and the amplitude control voltage V_(AMP) is input to a gateterminal thereof.

The drive circuit unit 6 includes a PMOS transistor 30 and ahigh-voltage PMOS transistor 31 constituting a current mirror circuit,and a high-voltage NMOS transistor 32 connected to a source terminal ofthe PMOS transistor 30. A source terminal of the high-voltage NMOStransistor 32 is connected to a current source 33 that outputs a currentsignal in which two values including zero and a predetermined drivecurrent Ib are alternately output. The transducer 103 and a loadresistor 34 are connected to a drain terminal of the high-voltage PMOStransistor 31. The high-voltage NMOS transistor 32 is disposed toprotect a withstand voltage of the current signal 33.

A transmission control signal output from the transmission control unit101 is added to the current source 33. When the transmission controlsignal is added, the current source 33 outputs the drive current Ib. Thedrive circuit unit 6 outputs the current signal output from the currentsource 33 to the transducer 103 as a drive current, and drives thetransducer 103. When the voltage of the transducer 103 is V_(OUT) andthe drive current is zero, the load resistor 34 discharges an electriccharge of the transducer 103, and changes a potential of the transducer103 to a ground level.

A High level voltage value of the output signal V_(OUT) to thetransducer 103 from the drive circuit unit 6 changes in conjunction withthe amplitude control voltage V_(AMP). Since the amplitude controlvoltage V_(AMP) is a voltage obtained by attenuating the power supplyvoltage HVDD by the set attenuation degree, the output signal V_(OUT) tothe transducer 103 also has an amplitude corresponding to the amplitudecontrol voltage V_(AMP). Accordingly, since an ultrasonic signal outputfrom the transducer 103 has an intensity corresponding to the amplitudecontrol voltage V_(AMP), the intensity is weighted by attenuating thedrive signal V_(OUT) with a predetermined attenuation degree.

In order to focus the ultrasonic beam at a transmission focus, it isnecessary to delay the drive signal for each transducer 103 according tothe position of the transmission focus. Therefore, the transmissioncontrol unit 101 outputs the transmission control signal at a timingdelayed according to the position of the transmission focus.

Therefore, when the intensity of the ultrasonic beam transmitted fromthe plurality of transducers 103 is changed, it is possible to performweighting for each transducer only by changing the power supply voltageHVDD without calculating the amplitude of the drive signal for eachtransducer. For example, by setting the output of the transducer locatedat the center of the ultrasonic beam to 100% and reducing the output ofthe transducer as it is away from the center, an ultrasonic beam withreduced side lobes can be transmitted.

At this time, the control unit 122 scans (moves) the position of theultrasonic beam for each transmission as necessary. Accordingly, sincethe position of the transducer 103 at the center of the ultrasonic beamis shifted, it is necessary to set the attenuation degree setting signalaccording to the attenuation degree of the transducer. The transmissioncontrol unit 101 receives information for defining a center position ofthe ultrasonic beam and the attenuation degree of each transducer 103 atthat time from the control unit 122 in advance and stores theinformation in a memory 101 a incorporated therein. When receiving aninstruction to scan (move) the center position of the ultrasonic beamfrom the control unit 122, the transmission control unit 101 reads theattenuation degree for each transducer 103 from the memory 101 a,generates an attenuation degree setting signal indicating theattenuation degree, and sets an amplitude control voltage in theamplitude control voltage generation unit 100 of each transducer 103.

The control unit 122 controls the variable voltage power supply 121 tofluctuate the voltage HVDD according to the imaging mode when switchingthe imaging mode as in the B mode and the color Doppler. Specifically,for example, a voltage for B-mode imaging is switched to a voltage forcolor Doppler imaging. When a B-mode image and a color Doppler image aresimultaneously imaged, the voltage HVDD is switched from the voltage forB-mode imaging to the voltage for color Doppler imaging a plurality oftimes per second.

Accordingly, the intensity varies according to the imaging mode, andappropriately weighted ultrasonic beams can be transmitted from theplurality of transducers 103 to the subject.

An echo of the ultrasonic beam generated in the subject for eachtransmission is received by the plurality of transducers 103. Areception signal is transferred to the reception unit 105 via thetransmission and reception separation unit 104, and receptionbeamforming processing or Doppler frequency determination processing isimplemented according to the imaging mode. Accordingly, focus data orDoppler frequency data is generated for a plurality of receptionfocuses. The B-mode image or the color Doppler image is generatedaccording to the imaging mode by using data in the image processing unit106. The generated image is displayed on the display unit 107.

In the above configuration, although for the sake of simplicity ofcalculation, the case where the resistance value R_(ref)′ of thereference resistor 14 and the resistance value R_(ref) of the referenceresistor 21 are equal (R_(ref)=R_(ref)′) is described as an example, thetwo resistance values may be different.

Although the current control unit 3 controls the attenuation degree ofthe amplitude control voltage according to the sum of the amplificationfactors n of the NMOS transistors 18 a to 18 n that are turned on amongthe switches 19 a to 19 n, the same effect can be obtained even when theresistance values of the reference resistor 14 and the resistors 11 and10 of the reference voltage generation unit 1 are variable.

Further, the above embodiment merely shows one embodiment, and theinvention is not limited as long as the amplitude control voltage can begenerated from a reference current having a linear relationship with thepower supply voltage.

In the configuration described above, the number of the transmissioncircuit unit 102 and the transmission and reception unit 104 is the sameas that of the plurality of ultrasonic transducers 103. The number ofthe amplitude control voltage generation unit 100 may be the same as thenumber of the transmission circuit unit 102, or one amplitude controlvoltage generation unit 100 may be disposed for a plurality oftransmission circuit units 102 when the plurality of transducers 103 aredriven at the same amplitude.

Whether the transmission unit 120 is disposed on an ultrasonic probeside or on a main body side will be described in fourth and fifthembodiments.

Second Embodiment

An ultrasonic imaging apparatus according to a second embodiment will bedescribed. In the first embodiment described above, a drive signal whosevoltage waveform changes between zero and a positive voltage V_(out) isgenerated. In the second embodiment, a drive signal whose voltagewaveform changes in three values including a negative voltage V_(OUTL),a positive voltage V_(OUTH), and a zero level is generated. Accordingly,a positive and negative symmetric waveform can be generated, and THIimaging using pulse-in version can be performed.

In the ultrasonic imaging apparatus according to the second embodiment,the same components as those of the ultrasonic imaging apparatusaccording to the first embodiment are denoted by the same referencenumerals and the description thereof is omitted, and a configurationdifferent from that of the first embodiment will be described below.

In the second embodiment, the variable voltage power supply 121 outputsa positive voltage and a negative voltage. The amplitude control voltagegeneration unit 100 generates two types of amplitude control voltages: apositive-side amplitude control voltage and a negative-side amplitudecontrol voltage. The transmission circuit unit 102 reduces an absolutevalue of the positive voltage output from the variable voltage powersupply 121 to a value corresponding to the positive-side amplitudecontrol voltage, reduces an absolute value of the negative voltage to avalue corresponding to the negative-side amplitude control voltage, andgenerates a drive signal with the positive voltage after reduction as apositive-side amplitude and the negative voltage after reduction as anegative-side amplitude.

FIG. 6 shows a specific configuration of the transmission unit 120 ofthe ultrasonic imaging apparatus according to the second embodiment. Asin the first embodiment, the transmission unit 120 includes theamplitude control voltage generation unit 100 and the transmissioncircuit unit 102. The variable voltage power supply 121 includes avariable voltage power supply 121 a that supplies a positive voltage anda variable voltage power supply 121 b that supplies a negative voltage.

The amplitude control voltage generation unit 100 includes the referencevoltage generation unit 1 and the voltage-current conversion unit 2similar to those in the first embodiment, a current control unit 3 a anda positive-side current-voltage conversion unit 4 a that performpositive-side amplitude control, and a current control unit 3 b and anegative-side current-voltage conversion unit 4 b that performnegative-side amplitude control. The positive-side current control unit3 a and the positive-side current-voltage conversion unit 4 a have thesame configuration as the current control unit 3 and the current-voltageconversion unit 4 of the first embodiment, and generate a positive-sideamplitude control voltage. The negative-side current control unit 3 band the negative-side current voltage conversion unit 4 b havesubstantially the same configuration as the current control unit 3 andthe current-voltage conversion unit 4 of the first embodiment, butgenerate a negative-side amplitude control voltage.

That is, the amplitude control voltage generation unit 100 divides anoutput of the voltage-current conversion unit into the current controlunit 3 a that performs the positive-side amplitude control and thecurrent control unit 3 b that performs the negative-side amplitudecontrol, and generates the positive-side amplitude and the negative-sideamplitude individually by the current voltage conversion units 4 a and 4b. Here, the reference voltage generation unit 1 and the voltage-currentconversion unit 2 are disposed in common without being distinguishedbetween positive and negative, and the negative-side current controlunit 3 b generates a negative-side amplitude control voltage using thereference current I₀ same as the positive side.

In addition to a positive-side amplitude control unit 5 a and apositive-side drive circuit unit 6 a, the transmission circuit unit 102includes a negative-side amplitude control unit 5 b and a negative-sidedrive circuit unit 6 b connected to the negative variable voltage powersupply 121 b. The positive-side amplitude control unit 5 a and thenegative-side amplitude control unit 5 b are independently input withthe positive-side amplitude control voltage and the negative-sideamplitude control voltage. A positive-side drive voltage V_(OUTH) signaland a negative-side drive voltage V_(OUTL) signal respectively outputfrom the positive-side drive circuit unit 6 a and the negative-sidedrive circuit unit 6 b are input to a common signal line by shifting aphase of a peak position of a pulse. Thus, a drive signal whose waveformchanges between the negative voltage V_(OUTL) and the positive voltageV_(OUTH) is generated. The drive signal is supplied to the transducer103 to drive the transducer 103. Accordingly, amplitude control that isasymmetrical between positive and negative can be performed, and a drivesignal having a complicated waveform can be generated.

A specific circuit configuration example of the amplitude controlvoltage generation unit 100 is shown in FIG. 7. Circuit configurationsof the reference voltage generation unit 1, the voltage-currentconversion unit 2, the positive-side current control unit 3 a, thepositive-side current-voltage conversion unit 4 a, and the currentmirror circuits (15, 16) that connect the voltage-current conversionunit 2 and the positive-side current control unit 3 a to supply thereference current I₀ are the same as those of the reference voltagegeneration unit 1, the voltage-current conversion unit 2, the currentcontrol unit 3, the current-voltage conversion unit 4 and the currentmirror circuits (15, 16) of FIG. 4 according to the first embodiment.

The negative-side current control unit 3 b includes the plurality ofNMOS transistors 18 a to 18 n, and constitutes a current mirror with thePMOS transistor 15. Therefore, although a semiconductor type of thetransistor in the negative-side current control unit 3 b is differentfrom that in the positive-side current control unit 3 a including theNMOS transistor 17 and the plurality of NMOS transistors 18 a to 18 nhaving different sizes, the circuit configurations thereof are the same.

The negative-side current-voltage conversion unit 4 b has aconfiguration in which a high withstand voltage PMOS transistor 24 and areference resistor 25 are connected in series and the negative-sidevariable voltage power supply 121 b is connected to the referenceresistor 25. Therefore, although a semiconductor type of the transistorin the negative-side current-voltage conversion unit 4 b is differentfrom that in the positive-side current-voltage conversion unit 4 a inwhich the high withstand voltage transistor 20 and the referenceresistor 21 are connected, the circuit configurations thereof are thesame.

When PMOS transistors 22 a to 22 n of the negative-side current controlunit 3 b are turned on and off according to an attenuation degreesetting signal output from the transmission control unit 101 by switches23 a to 23 n, a current I₀″ that is a sum of currents flowing throughthe turned-on PMOS transistors is output from the PMOS transistors 22 ato 22 n as an output of the current control unit 3. Therefore, thecurrent I₀, which is an input signal to the current control unit 3 b, isamplified to the current I₀′ and output. When a sum of amplificationfactors of the PMOS transistors 22 a to 22 n connected to one or moreswitches turned on according to the attenuation amount setting signal ism, and a voltage of the negative-side variable voltage power supply 121b is HVSS, the negative-side amplitude control voltage V_(AMPL) isexpressed by Formula (8). In the Formula (8), as an example, thenegative-side voltage HVSS is equal to an absolute value of thepositive-side variable voltage power supply HVDD.V _(AMPL)=HVSS(1−m×R ₂/(R ₁ +R ₂))  (8)

A circuit configuration example of the transmission circuit unit 102that can output positive and negative voltages is shown in FIG. 8. Thepositive-side amplitude control unit 5 a and the positive-side drivecircuit unit 6 a are the same as the circuit configurations of theamplitude control unit 5 and the drive circuit unit 6 of FIG. 5according to the first embodiment. The negative-side amplitude controlunit 5 b includes a high-voltage PMOS transistor, and the drive circuitunit 6 b includes a high withstand voltage PMOS transistor 36, an NMOStransistor 38, and a high withstand voltage NMOS transistor 35 thatconvert a voltage level.

A transmission control signal output from the transmission control unit101 is added to the current sources 33 and 37. When outputting an Hlevel, the current source 33 is turned on, and when outputting an Llevel, the current source 37 is turned on. By repeating the twoprocessing alternately, it is possible to drive the ultrasonictransducer 103 with an H level V_(OUTH) and an L level V_(OUTL). Whenboth the current sources 33 and 37 are turned off, a zero level isoutput by the load resistor 34. At this time, V_(OUTH) and V_(OUTL)signal levels change in conjunction with the positive and negativeamplitude control voltages V_(AMPH) and V_(AMPL). The amplitude controlvoltage V_(AMPH) is a voltage obtained by attenuating the power supplyvoltage HVDD by a set attenuation degree, and the amplitude controlvoltage V_(AMPL) is a voltage obtained by attenuating the power supplyvoltage HVSS by a set attenuation degree, so that the output signalsV_(OUTH) and V_(OUTL) to the transducer 103 also have amplitudesrespectively corresponding to the amplitude control voltages V_(AMPH)and V_(AMPL). Even when the voltages of the variable voltage powersupplies 121 a and 121 b are fluctuated, the amplitude control voltagesV_(AMPH) and V_(AMPL) are voltages proportional to the power supplyvoltages HVDD and HVSS, in which the power supply voltage is attenuatedby the attenuation degree indicated by the attenuation degree settingsignal, so that amplitude control reflecting the magnitude of the powersupply voltage and the attenuation degree (weighting) can be performed.

In the above description, the positive-side power supply voltage HVDDand the negative-side power supply voltage HVSS are equal in magnitude.However, in the case of different voltages, the reference voltagegeneration unit 1 and the voltage current conversion unit 2 may bedisposed independently of each other. A transmission circuit whoseattenuation degree is constant even when the positive-side power supplyHVDD and the negative-side power supply HVSS are different can beprovided.

Third Embodiment

Next, a third embodiment will be described. In the first embodiment, theamplitude control voltage V_(AMP) is a voltage value obtained byattenuating the output voltage HVDD of the variable voltage power supply121 with the set attenuation degree as in Formula (6). However, thevoltage V_(OUT) applied to the ultrasonic transducer 103 may bedifferent from the amplitude control voltage V_(AMP) due to an offsetvoltage generated by the amplitude control unit 5 of the transmissioncircuit unit 102. For example, in the transmission circuit unit 102shown in FIG. 5, the H level V_(OUTH) of the output V_(OUT) causes apotential difference between the gate terminal and the source terminalof the NMOS transistor of the amplitude control unit since a current ofthe current source 33 also flows in the amplitude control unit 5 in aHigh period. Therefore, when a gate-source voltage is V_(GS), therelationship between V_(OUTH) and V_(AMP) is expressed by Formula (9).V _(OUTH) =V _(AMP) −V _(GS)  (9)

Since V_(GS) is a constant voltage that does not depend on the voltageHVDD of the variable voltage power supply, when the power supply voltageHVDD of the transmission circuit unit 102 is small, or when theattenuation degree is set large, V_(GS) cannot be ignored and is outputas an error from the set attenuation amount. Therefore, in the thirdembodiment, as shown in FIG. 9, a fixed current generation unit 7 isprovided in the amplitude control voltage generation unit 100, and acurrent corresponding to the offset voltage V_(GS) is added to theoutput current from the current control unit 3 to cancel the error inthe offset voltage V_(GS).

FIG. 10 shows a specific configuration example. In a circuitconfiguration similar to that of the amplitude control voltagegeneration unit 100 in FIG. 4, a fixed offset current source 26independent of the power supply voltage HVDD of the variable voltagepower supply 121 is connected between the switches 19 a to 19 n of thecurrent control unit 3 and a source of the high withstand voltage NMOStransistor 20 of the current-voltage conversion unit 4 to supply anoffset current I_(off). With the above circuit configuration, theamplitude control voltage V_(AMP) is expressed by Formula (10) and theoutput voltage V_(OUTH) is expressed by Formula (11).V _(AMP)=HVDD(1−n×R ₂/(R ₁ +R ₂))+R ₂ ×I _(off)  (10)V _(OUTH)=HVDD(1−n×R ₂/(R ₁ +R ₂))+R ₂ ×I _(off) −V _(GS)  (11)

Therefore, if the magnitude of the offset current I_(off) is set suchthat V_(GS)=R₂×I_(off)′ the output voltage V_(OUTH) is set as follows:V _(OUTH)=HVDD(1−n×R ₂/(R ₁ +R ₂)).

Therefore, the output voltage of the transmission circuit unit 102 canbe more accurately attenuated according to the set attenuation degree.

In the above description, the operation of the output voltage V_(OUTH)is described only on the positive side. However, for the output voltageV_(OUTL) of the second embodiment, the offset voltage can be similarlycancelled.

In addition, since the offset voltage V_(GS) may fluctuate due totemperature characteristics and manufacturing variations of the NMOStransistor, when using the variable current source 26 in which theoffset current I_(off) changes in conjunction with the fluctuation ofthe offset voltage V_(GS), the offset voltage V_(GS) can be canceledwith higher accuracy and the accuracy of the attenuation degree of theoutput voltage can be improved.

Fourth Embodiment

As a fourth embodiment, an example of an appearance of an ultrasoundsystem is shown in FIG. 11.

The ultrasonic diagnostic apparatus includes a main frame (apparatusmain body) 201, an ultrasonic probe 203, and a cable 202 connecting themain frame 201 and the ultrasonic probe 203. The image display unit 107is mounted and connected to the main frame 201.

In the present embodiment, the transducer 103 is disposed in theultrasonic probe 203, and the transmission unit 120 is disposed insidethe main frame 201. The transmission unit 120 and the transducer 103 areconnected to each other via a wiring inside the cable 202. Therefore,the amplitude control voltage generation unit 100 and the transmissioncircuit unit 102 are disposed inside the main frame 201.

As described in the first to third embodiments, even when the voltage ofthe variable voltage power supply 121 is changed, the amplitude controlvoltage generation unit 100 and the transmission circuit unit 102 of thetransmission unit 120 of the present embodiment have a simple circuitconfiguration that does not need to calculate a voltage value of a drivesignal by calculation, and can be attenuated with a set attenuationdegree, and thus a circuit scale thereof is small. Therefore, bydisposing the amplitude control voltage generation unit 100 and thetransmission circuit unit 102 in the main frame 201, it is possible torealize a small main frame.

In the above configuration, since the drive signal attenuated for eachof the plurality of transducers 103 is output from the transmissioncircuit unit 102 of the main frame 201 to the transducer 103 of theultrasonic probe 203 via the cable 202, a dedicated line is preferablydisposed as the cable 202.

Fifth Embodiment

As a fifth embodiment, another example of the appearance of theultrasound system is shown in FIG. 11.

The ultrasonic diagnostic apparatus of the fifth embodiment includes themain frame (apparatus main body) 201, the ultrasonic probe 203, and thecable 202. The image display unit 107 is mounted and connected to themain frame 201. The transmission unit 120 is disposed in the ultrasonicprobe 203.

As described in the first to third embodiments, even when the voltage ofthe variable voltage power supply 121 is changed, the vibration controlvoltage generation unit 100 and the transmission circuit unit 102 of thetransmission unit 120 of the present embodiment have a simple circuitconfiguration that does not need to calculate a voltage value of a drivesignal by calculation, and can be attenuated with a set attenuationdegree, and thus a circuit scale thereof is small. Therefore, it ispossible to dispose the transducer 103 in the ultrasonic probe 203, andit is possible to provide the small ultrasonic probe 203.

In addition, since the transmission unit 120 is disposed in theultrasonic probe 203, the cable 202 only needs to be a cable for acontrol signal between the transmission control unit 101 and the controlunit 122 and a cable for supplying a power supply voltage for thetransmission unit 120, and the number of the cable can be reduced, andthe size of the cable 202 can be reduced.

In the fourth and fifth embodiments, the transducers 103 disposed in theultrasonic probe 203 may be arranged in M×N two-dimensional arrays. Atthis time, as shown in FIG. 13, the transmission circuit unit 102 and adelay circuit that is a part of the reception unit 105 are connected tothe transducers 103 as the analog front end circuit 41. Thus, byarranging the transducers 103 in two dimensions and adjusting thetransmission focus and the reception focus, a three-dimensionalultrasonic image can be generated.

As shown in FIG. 13, the analog front end circuits 41 for respectivetransducers 103 arranged by M×N are formed on the same semiconductorsubstrate and integrated as a beamformer LSI 40 together with a delaycontrol unit of the reception unit 105 and the amplitude control voltagegeneration unit 100.

At this time, as shown in FIG. 13, the amplitude control voltagegeneration units 100 may be disposed at ends of rows of the M×N analogfront end circuits 41 and supply the amplitude control voltage to theplurality of transmission circuit units 102.

An example of a change in the transmission signal is shown in FIG. 14 asa schematic diagram. From a time t1 in FIG. 14(a) to a time t2 in FIG.14(b), a center position of the ultrasonic beam to be transmitted isshifted in a row direction, and a transmission signal level for eachtransducer due to apodization also changes accordingly. In this way, asthe transducer is away from the center of the ultrasonic beam to betransmitted, the attenuation degree of the amplitude is set to begradually increased, and the center position of the ultrasonic beam ismoved together with time. This makes it possible to perform ultrasonicbeam scanning while reducing the side lobes of the ultrasonic beam.

REFERENCE SIGN LIST

-   1 reference voltage generation unit-   2 voltage-current conversion unit-   3 current control unit-   3 a, 3 b current control unit-   4 current-voltage conversion unit-   4 a, 4 b current-voltage conversion unit-   5 amplitude control unit-   5 a, 5 b amplitude control unit-   6 drive circuit unit-   6 a, 6 b drive circuit unit-   7 fixed current generation unit-   10, 11 resistor-   12 operational amplifier (OPAMP)-   13, 17, 18 a to 18 n N-type MOS (NMOS) transistor-   14, 25 reference resistor-   15, 16, 22 a to 22 n P-type MOS (PMOS) transistor-   19 a to 19 n, 23 a to 23 n switch-   20 high withstand voltage NMOS transistor-   21 high withstand voltage PMOS transistor-   24 high withstand voltage PMOS transistor-   26 fixed current source-   30 PMOS transistor-   31, 36 high withstand voltage PMOS transistor-   32, 35 high withstand voltage NMOS transistor-   33, 37 current source-   33 current source-   34 load resistor-   38 NMOS transistor-   40 beamformer LSI-   41 analog front end circuit-   100 amplitude control voltage generation unit-   101 transmission control unit-   101 a memory-   102 transmission circuit unit-   103 transducer-   104 transmission and reception separation unit-   105 reception unit-   106 image processing unit-   107 display unit-   120 transmission unit-   121 variable voltage power supply-   122 control unit-   201 main frame-   202 cable-   203 ultrasonic probe

The invention claimed is:
 1. An ultrasonic imaging apparatus comprising:a plurality of transducers that transmit ultrasonic waves; and atransmission unit that supplies drive signals to the plurality oftransducers, wherein the transmission unit includes an amplitude controlvoltage generation unit and a transmission circuit unit, and theamplitude control voltage generation unit and the transmission circuitunit are connected to a common voltage power supply, wherein theamplitude control voltage generation unit includes a current mirrorcircuit including an NMOS transistor and a plurality of NMOS transistorsand switches respectively connected to the NMOS transistors, wherein theamplitude control voltage generation unit receives an output voltage ofthe voltage power supply and an attenuation degree setting signalinstructing an attenuation degree of the drive signal for each of thetransducers for weighting for the drive signal, and generates anamplitude control voltage corresponding to a voltage obtained byattenuating the output voltage of the voltage power supply by theattenuation degree based on a sum of the NMOS transistors turned onaccording to the switches which are switched based on the an attenuationdegree setting signal, and the transmission circuit unit reduces anabsolute value of the output voltage of the voltage power supply to avalue corresponding to the amplitude control voltage, and generates adrive signal having a predetermined waveform whose amplitude is thevoltage after the reduction for each of the transducers.
 2. Theultrasonic imaging apparatus according to claim 1, wherein the outputvoltage of the voltage power supply is variable and is changed accordingto an imaging mode, which is at least one of a B-mode imaging and colorDoppler imaging.
 3. The ultrasonic imaging apparatus according to claim1, wherein the transmission circuit unit and the amplitude controlvoltage generation unit are disposed for each of the transducers.
 4. Theultrasonic imaging apparatus according to claim 1, wherein the amplitudecontrol voltage generation unit includes a reference voltage generationunit that generates a reference voltage from the output voltage of thevoltage power supply, a voltage-current conversion unit that convertsthe reference voltage into a current, and a current-voltage conversionunit that generates the amplitude control voltage by converting thecurrent attenuated by the current control unit into a voltage.
 5. Theultrasonic imaging apparatus according to claim 1, further comprising: atransmission control unit that generates the attenuation degree settingsignal for each of the transducers and outputs the signal to theamplitude control voltage generation unit.
 6. The ultrasonic imagingapparatus according to claim 1, wherein the voltage power supply outputsa positive voltage and a negative voltage, the amplitude control voltagegeneration unit generates, as the amplitude control voltage, two typesof amplitude control voltages, that is, a positive-side amplitudecontrol voltage and a negative-side amplitude control voltage, and thetransmission circuit unit reduces an absolute value of the positivevoltage output from the voltage power supply to a value corresponding tothe positive-side amplitude control voltage, reduces an absolute valueof the negative voltage to a value corresponding to the negative-sideamplitude control voltage, and generates the drive signal with thepositive voltage after the reduction as a positive-side amplitude andthe negative voltage after the reduction as a negative-side amplitude.7. The ultrasonic imaging apparatus according to claim 4, furthercomprising: a current source that adds a current for canceling an offsetvoltage generated by the transmission circuit unit to a current outputfrom the current control unit.
 8. The ultrasonic imaging apparatusaccording to claim 1, further comprising: an apparatus main body and anultrasonic probe connected to the apparatus main body by a cable,wherein the transducer, the transmission circuit unit, and the amplitudecontrol voltage generation unit are disposed in the ultrasonic probe. 9.An ultrasonic probe comprising: a plurality of transducers that transmitultrasonic waves; and a transmission unit that supplies drive signals tothe plurality of transducers, wherein the transmission unit includes anamplitude control voltage generation unit and a transmission circuitunit, and the amplitude control voltage generation unit and thetransmission circuit unit are connected to a common voltage powersupply, wherein the amplitude control voltage generation unit includes acurrent mirror circuit including an N-type metal-oxide-semiconductor(NMOS) transistor and a plurality of NMOS transistors and switchesrespectively connected to the NMOS transistors, wherein the amplitudecontrol voltage generation unit receives an output voltage of thevoltage power supply and an attenuation degree setting signalinstructing an attenuation degree of the drive signal for each of thetransducers for weighting for the drive signal, and generates anamplitude control voltage corresponding to a voltage obtained byattenuating the output voltage of the voltage power supply by theattenuation degree based on a sum of the NMOS transistors turned onaccording to the switches which are switched based on the an attenuationdegree setting signal, and the transmission circuit unit reduces anabsolute value of the output voltage of the voltage power supply to avalue corresponding to the amplitude control voltage, and generates adrive signal having a predetermined waveform whose amplitude is thevoltage after the reduction for each of the transducers.
 10. Atransmission apparatus that supplies drive signals to a plurality oftransducers that transmit ultrasonic waves, the transmission apparatuscomprising: an amplitude control voltage generation unit, and atransmission circuit unit, wherein the amplitude control voltagegeneration unit and the transmission circuit unit are connected to acommon voltage power supply, wherein the amplitude control voltagegeneration unit includes a current mirror circuit including an NMOStransistor and a plurality of NMOS transistors and switches respectivelyconnected to the NMOS transistors, wherein the amplitude control voltagegeneration unit receives an output voltage of the voltage power supplyand an attenuation degree setting signal instructing an attenuationdegree of the drive signal for each of the transducers for weighting forthe drive signal, and generates an amplitude control voltagecorresponding to a voltage obtained by attenuating the output voltage ofthe voltage power supply by the attenuation degree based on a sum of theNMOS transistors turned on according to the switches which are switchedbased on the an attenuation degree setting signal, and the transmissioncircuit unit reduces an absolute value of the output voltage of thevoltage power supply to a value corresponding to the amplitude controlvoltage, and generates a drive signal having a predetermined waveformwhose amplitude is the voltage after the reduction for each of thetransducers.